#include <torch/extension.h>

#include <string>

// CUDA forward declarations

std::vector<at::Tensor> softmax_xentropy_cuda(
    const at::Tensor &input,
    const at::Tensor &labels,
    const float smoothing,
    const bool half_to_float);

at::Tensor softmax_xentropy_backward_cuda(
    const at::Tensor &grad_loss,
    const at::Tensor &logits,
    const at::Tensor &max_log_sum_exp,
    const at::Tensor &labels,
    const float smoothing);

// C++ interface

#define CHECK_CUDA(x) TORCH_CHECK(x.is_cuda(), #x " must be a CUDA tensor")
#define CHECK_CONTIGUOUS(x) TORCH_CHECK(x.is_contiguous(), #x " must be contiguous")
#define CHECK_INPUT(x) CHECK_CUDA(x); CHECK_CONTIGUOUS(x)

std::vector<at::Tensor> softmax_xentropy_forward(
    const at::Tensor &input,
    const at::Tensor &labels,
    const float smoothing,
    const bool half_to_float) {
    CHECK_CUDA(input);
    CHECK_INPUT(labels);

    return softmax_xentropy_cuda(input, labels, smoothing, half_to_float);
}

at::Tensor softmax_xentropy_backward(
    const at::Tensor &grad_loss,
    const at::Tensor &logits,
    const at::Tensor &max_log_sum_exp,
    const at::Tensor &labels,
    const float smoothing)  {
    CHECK_CUDA(grad_loss);
    CHECK_CUDA(logits);
    CHECK_INPUT(max_log_sum_exp);
    CHECK_INPUT(labels);

    return softmax_xentropy_backward_cuda(grad_loss, logits, max_log_sum_exp, labels, smoothing);
}

PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
    m.def("forward", &softmax_xentropy_forward, "Softmax cross entropy loss with label smoothing forward (CUDA)", py::call_guard<py::gil_scoped_release>());
    m.def("backward", &softmax_xentropy_backward, "Softmax cross entropy loss with label smoothing backward (CUDA)", py::call_guard<py::gil_scoped_release>());
    // ref: https://pybind11.readthedocs.io/en/stable/basics.html#exporting-variables
    py::object version = py::cast(
#ifdef XENTROPY_VER
        XENTROPY_VER
#else
        std::string{}
#endif
        );
    m.attr("__version__") = version;
}
